Falling film evaporator

ABSTRACT

Falling film and hybrid falling film evaporators are provided for use in a two-phase refrigeration system or process system. The evaporator includes a shell having an upper portion, a lower portion, and a tube bundle having tubes extending substantially horizontally in the shell. A hood disposed over the tube bundle has an upper end adjacent the upper portion above the tube bundle, the upper end having opposed substantially parallel walls extending toward the lower portion, the walls terminating at an open end opposite the upper end. Once liquid refrigerant or liquid refrigerant and vapor refrigerant is deposited onto the tube bundle, the substantially parallel walls of the hood substantially prevent cross flow of refrigerant vapor or liquid and vapor between the tubes of the tube bundle. A flow distributor disposed adjacent the open end between the hood and the shell modifies the refrigerant flow, providing more uniform refrigerant flow distribution.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.60/871,303 and 60/890,473, filed Dec. 21, 2006 and Feb. 17, 2007,respectively.

BACKGROUND

The present application relates generally to falling film and hybridfalling film evaporator systems in refrigeration, air conditioning andchilled water systems or process systems.

Certain process systems, as well as refrigeration, air conditioning andchilled water systems, include an evaporator to effect a transfer ofthermal energy between refrigerant of the system and another fluid to becooled. One type of evaporator includes a shell with a plurality oftubes forming a tube bundle through which the fluid to be cooled iscirculated. The refrigerant is brought into contact with the outer orexterior surfaces of the tube bundle inside the shell, resulting in athermal energy transfer between the fluid to be cooled and therefrigerant. In a conventional evaporator, the refrigerant is heated andconverted to a vapor state, which is then returned to a compressor wherethe vapor is compressed, to begin another refrigerant cycle. The cooledfluid is circulated to a plurality of heat exchangers located throughoutthe building. Warmer air is passed over the heat exchangers where thecooled fluid is being warmed, while cooling the air for the buildingreturned to the evaporator to repeat the process.

For example, some types of evaporators with refrigerant boiling outsidethe tubes include flooded evaporators, falling film evaporators andhybrid falling film evaporators. In conventional flooded evaporators,the shell is partially filled with a pool of boiling liquid refrigerantin which the tube bundle is immersed.

In a conventional falling film evaporator, a dispenser deposits, such asby spraying, an amount of liquid refrigerant onto the surfaces of thetubes of the tube bundle from a position above the tube bundle, forminga layer (or film) of liquid refrigerant on the tube surface. Therefrigerant in a liquid or two-phase liquid and vapor state contacts theupper tube surfaces of the tube bundle, and by force of gravity, fallsvertically onto the tube surfaces of lower disposed tubes.

A conventional hybrid falling film evaporator incorporates theattributes of a falling film evaporator and a flooded evaporator byimmersing a lesser proportion of the tubes of the tube bundle than theflooded evaporator while still spraying fluid on the upper tubes,similar to a falling film evaporator.

One challenge to the efficient operation of the falling film and hybridfalling film evaporators is that a portion of the fluid vaporizes andsignificantly expands in volume. The vaporized fluid expands in alldirections, causing cross flow, or travel by the vaporized fluid in adirection that is transverse, or at least partially transverse to thevertical flow direction of the liquid fluid under the effect of gravity.Cross flow results in insufficient wetting of tubes of the tube bundle,significantly reducing heat transfer with the fluid to be cooled flowinginside those tubes in the tube bundle.

Another challenge is the compressor, which receives its supply ofvaporized fluid from an outlet typically formed in the upper portion ofthe evaporator, can be damaged if the vaporized fluid contains entrainedliquid droplets. Components must be implemented to provide separationbetween the vapor and liquid droplets. However, these components add tothe complexity and cost of the system, and may also result in anundesired pressure drop prior to the vapor refrigerant reaching thecompressor.

What are needed are falling film and hybrid falling film evaporatorsthat substantially prevent cross flow caused by expanding vaporizingfluid and which also require less space than a flooded evaporator forliquid droplet separation than a conventional flooded or existingdesigns of flooded film or hybrid evaporators.

Intended advantages of the disclosed systems and/or methods satisfy oneor more of these needs or provides other advantageous features. Otherfeatures and advantages will be made apparent from the presentspecification. The teachings disclosed extend to those embodiments thatfall within the scope of the claims, regardless of whether theyaccomplish one or more of the aforementioned needs.

SUMMARY

The present application relates to a refrigeration system including acompressor, a condenser, an expansion device and an evaporator connectedin a closed refrigerant loop. The evaporator includes a shell having anupper portion and a lower portion and a tube bundle, the tube bundlehaving a plurality of tubes extending substantially horizontally in theshell. A hood is disposed over the tube bundle, the hood having a closedend and an open end opposite the closed end, the closed end beingdisposed above the tube bundle adjacent the upper portion of the shell.The hood further has opposed substantially parallel walls extending fromthe closed portion toward the open portion of the shell. A refrigerantdistributor is disposed below the hood and above the tube bundle, therefrigerant distributor being configured to deposit liquid refrigerantor liquid and vapor refrigerant onto the tube bundle. The substantiallyparallel walls of the hood substantially prevent cross flow of therefrigerant between the plurality of tubes of the tube bundle. A flowdistributor is disposed adjacent the open end between the hood and theshell. The flow distributor modifies the refrigerant flow between thehood and the shell to provide a more uniform refrigerant flowdistribution.

The present application further relates to a falling film evaporator foruse in a refrigeration system including a shell having an upper portionand a lower portion. A tube bundle has a plurality of tubes extendingsubstantially horizontally in the shell. A hood is disposed over thetube bundle, the hood having a closed end and an open end opposite theclosed end, the closed end being disposed above the tube bundle adjacentthe upper portion of the shell. The hood further has opposedsubstantially parallel walls extending from the closed portion towardthe open portion of the shell. A refrigerant distributor is disposedbelow the hood and above the tube bundle. The refrigerant distributor isconfigured to deposit liquid refrigerant or liquid and vapor refrigerantonto the tube bundle. The substantially parallel walls of the hoodsubstantially prevent cross flow of the refrigerant between theplurality of tubes of the tube bundle. A flow distributor is disposedadjacent the open end between the hood and the shell. The flowdistributor modifies the refrigerant flow between the hood and the shellto provide a more uniform refrigerant flow distribution.

The present application allows that the fluid distributor receivesrefrigerant at medium or high pressure, i.e., close to condensingpressure, and can be a two-phase liquid refrigerant and vaporrefrigerant. Under these conditions, the refrigerant mist and dropletsgenerated are contained below the hood and coalesced onto the tubes, aswell as the roof and walls of the hood, to prevent the refrigerant mistand droplets from becoming entrained into the suction line. In addition,a flow distributor reduces gas velocity exiting the hood by providing amore uniform flow distribution. This improved flow distribution helps tofurther reduce droplet entrainment in the refrigerant mist that couldreach the suction line.

The present application still further relates to a hybrid falling filmevaporator for use in a refrigeration system including a shell having anupper portion and a lower portion. A lower tube bundle is in fluidcommunication with an upper tube bundle, the lower and upper tubebundles each having a plurality of tubes extending substantiallyhorizontally in the shell, the lower tube bundle being at leastpartially submerged by refrigerant in the lower portion of the shell. Ahood is disposed over the upper tube bundle, the hood having a closedend and an open end opposite the closed end, the closed end beingadjacent the upper portion of the shell above the upper tube bundle. Thehood further has opposed substantially parallel walls extending from theclosed end toward the open end adjacent the lower portion of the shell.A refrigerant distributor is disposed above the upper tube bundle, therefrigerant distributor depositing refrigerant onto the upper tubebundle. The substantially parallel walls of the hood substantiallyprevent cross flow of refrigerant between the plurality of tubes of theupper tube bundle. A flow distributor is disposed adjacent the open endbetween the hood and the shell. The flow distributor modifies therefrigerant flow between the hood and the shell to provide a moreuniform refrigerant flow distribution.

The present application yet further relates to a falling film evaporatorfor use in a control process including a shell having an upper portionand a lower portion. A tube bundle has a plurality of tubes extendingsubstantially horizontally in the shell. A hood is disposed over thetube bundle, the hood having a closed end and an open end opposite theclosed end, the closed end being disposed above the tube bundle adjacentthe upper portion of the shell. The hood further has opposedsubstantially parallel walls extending toward the lower portion of theshell. A fluid distributor is disposed below the hood and above the tubebundle, the fluid distributor being configured to deposit liquid fluidor liquid and vapor fluid onto the tube bundle. The substantiallyparallel walls of the hood substantially prevent cross flow of the fluidbetween the plurality of tubes of the tube bundle. A flow distributor isdisposed adjacent the open end between the hood and the shell. The flowdistributor modifies the refrigerant flow between the hood and the shellto provide a more uniform refrigerant flow distribution.

The present application still further relates to a falling filmevaporator for use in a refrigeration system including a shell having anupper portion and a lower portion. A tube bundle has a plurality oftubes extending substantially horizontally in the shell. A hood isdisposed over the tube bundle, the hood having a closed end and an openend opposite the closed end. The closed end is disposed above the tubebundle adjacent the upper portion of the shell. The hood further hasopposed substantially parallel walls extending from the closed portiontoward the open portion of the shell. The hood is asymmetricallydisposed within the evaporator.

The present application yet further relates to a falling film evaporatorfor use in a refrigeration system including a shell having an upperportion and a lower portion. A tube bundle has a plurality of tubesextending substantially horizontally in the shell. A hood is disposedover the tube bundle, the hood having a closed end and an open endopposite the closed end. The closed end is disposed above the tubebundle adjacent the upper portion of the shell, the hood further havingopposed substantially parallel walls extending from the closed portiontoward the open portion of the shell. The hood includes surfacetextures.

An advantage of the present application is that it substantiallyprevents cross flow caused by expanding vaporizing fluid, facilitatingincreased heat transfer with a minimum re-circulation rate.

A still further advantage of the present application is that provides anefficient means of avoiding the carry-over of liquid droplets into thecompressor suction.

A still further advantage of the present application is that it is easyto manufacture and install.

A still yet further advantage of the present application is that it canaccommodate a mix of liquid and vapor at moderate or high pressure thatis applied by the distributor over the tube bundle.

A further advantage of the present application is that it can be usedwith either a falling film evaporator construction or a hybrid fallingfilm evaporator construction.

An additional advantage of the present application is that it canprovide a more uniform flow distribution of refrigerant to achieveimproved liquid separation.

Other features and advantages of the present application will beapparent from the following more detailed descriptions of embodiments,taken in conjunction with the accompanying drawings which illustrate, byway of example, the principles of the application. Skilled artisans willappreciate that elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale. For example,the dimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding of variousembodiments of the present application. Also, common but well-understoodelements that are useful or necessary in a commercially feasibleembodiment are typically not depicted in order to facilitate a lessobstructed view of these various embodiments of the present application.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an illustration of an exemplary HVAC&R system disposed in acommercial setting.

FIG. 2 is a schematic of a compressor system of the present application.

FIG. 3 is a cross section of an embodiment of a falling film evaporatorof the present application.

FIGS. 4-5 are cross sections of alternate embodiments of a falling filmevaporator of the present application.

FIG. 6 is a cross section of an embodiment of a hybrid falling filmevaporator of the present application.

FIG. 7 is a cross section of a further embodiment of a hybrid fallingfilm evaporator of the present application.

FIG. 8 is a cross section of a flow distribution device for anevaporator of the present application.

FIGS. 9-12 is a cross section of various embodiments of flowdistribution devices for an evaporator of the present application.

FIG. 13 is a cross section of a further embodiment of a hybrid fallingfilm evaporator of the present application.

FIG. 14 is a cross section of a further embodiment of a hybrid fallingfilm evaporator of the present application.

FIG. 15 is an elevation view of an embodiment of a hood taken along line17-17 of FIG. 14.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows an exemplary HVAC&R system configured for providing coolingto a commercial building BL. A chiller system CH circulates a cooledfluid CF through coils disposed in air handling units AH. Air handlingunits AH use ducting DU to draw outside ingested air OI that is mixedwith recirculated air within building BL. The cooled fluid CF cools themix of outside ingested air OI and recirculated air that is providedthroughout building BL by a distribution system DS to provide climatecontrol within building BL. A boiler system (not shown) may be used tocirculate a heated fluid for providing heating to the building BL.

FIG. 2 illustrates generally one system configuration of the presentapplication. A refrigeration or chiller system 10 includes an AC powersource 20 that supplies a combination variable speed drive (VSD) 30 andpower/control panel 35, which powers a motor 40 that drives a compressor60, as controlled by the controls located within the power/control panel35. It is appreciated that the term “refrigeration system” can includealternate constructions, such as a heat pump. In one embodiment of theapplication, all of the components of the VSD 30 are contained withinthe power/control panel 35. The AC power source 20 provides single phaseor multi-phase (e.g., three phase), fixed voltage, and fixed frequencyAC power to the VSD 30 from an AC power grid or distribution system thatis present at a site. The compressor 60 compresses a refrigerant vaporand delivers the vapor to the condenser 70 through a discharge line. Thecompressor 60 can be any suitable type of compressor, e.g., centrifugalcompressor, reciprocating compressor, screw compressor, scrollcompressor, etc. The refrigerant vapor delivered by the compressor 60 tothe condenser 70 enters into a heat exchange relationship with a fluid,such as water, flowing through a heat-exchanger coil or tube bundle 55connected to a cooling tower 50. However, it is to be understood thatcondenser 70 can be air-cooled or can use any other condensertechnology. The refrigerant vapor in the condenser 70 undergoes a phasechange to a refrigerant liquid as a result of the heat exchangerelationship with the liquid in the heat-exchanger coil 55. Thecondensed liquid refrigerant from condenser 70 flows to an expansiondevice 75, which greatly lowers the temperature and pressure of therefrigerant before entering the evaporator 80. Alternately, most of theexpansion can occur in a nozzle 108 (FIGS. 3-8) when used as a pressureadjustment device. A fluid circulated in heat exchange relationship withthe evaporator 80 can then provide cooling to an interior space.

The evaporator 80 can include a heat-exchanger coil 85 having a supplyline 85S and a return line 85R connected to a cooling load 90. Theheat-exchanger coil 85 can include a plurality of tube bundles withinthe evaporator 80. Water or any other suitable secondary refrigerant,e.g., ethylene, ethylene glycol, or calcium chloride brine, travels intothe evaporator 80 via return line 85R and exits the evaporator 80 viasupply line 85S. The liquid refrigerant in the evaporator 80 enters intoa heat exchange relationship with the water in the heat-exchanger coil85 to chill the temperature of the secondary refrigerant in theheat-exchanger coil 85. The refrigerant liquid in the evaporator 80undergoes a phase change to a refrigerant vapor as a result of the heatexchange relationship with the liquid in the heat-exchanger coil 85. Thevapor refrigerant in the evaporator 80 then returns to the compressor 60to complete the cycle.

It is noted that the chiller system 10 of the present application mayuse a plurality of any combination of VSDs 30, motors 40, compressors60, condensers 70, and evaporators 80.

Referring to FIG. 3, one embodiment of evaporator 80 is a falling filmevaporator. In this embodiment, evaporator 80 includes a substantiallycylindrical shell 100 having an upper portion 102 and a lower portion104 with a plurality of tubes forming a tube bundle 106 extendingsubstantially horizontally along the length of the shell 100. A suitablefluid, such as water, ethylene, ethylene glycol, or calcium chloridebrine flows through the tubes of the tube bundle 106. A distributor 108disposed above the tube bundle 106 distributes refrigerant fluid, suchas R134a received from the condenser 126 that is in a liquid state or atwo-phase liquid and vapor state, onto the upper tubes in the tubebundle 106. In other words, the refrigerant fluid can be in a two-phasestate, i.e., liquid and vapor refrigerant. In FIG. 4, the refrigerantdelivered to the distributor 108 is entirely liquid. In FIGS. 3, 5-7,the refrigerant delivered to the distributor 108 can be entirely liquidor a two-phase mixture of liquid and vapor. Liquid refrigerant that hasbeen directed through the tubes of the tube bundle 106 without changingstate collects adjacent the lower portion 104, this collected liquidrefrigerant being designated as liquid refrigerant 120. Although a pump95 can be used to re-circulate liquid refrigerant 120 from the lowerportion 104 to the distributor 108 (FIGS. 4 and 5), an ejector 128 canbe employed to draw the liquid refrigerant 120 from the lower portion104 using the pressurized refrigerant from condenser 126, which operatesby virtue of the Bernoulli effect, as shown in FIG. 3. In addition,while the level of the liquid refrigerant 120 is shown as being belowthe tube bundle 106 (e.g., FIGS. 3-5), it is to be understood that thelevel of the liquid refrigerant 120 may immerse a portion of the tubesof the tube bundle 106.

Further referring to FIG. 3, a hood 112 is disposed over the tube bundle106 to substantially prevent cross flow of vapor refrigerant or ofliquid and vapor refrigerant between the tubes of the tube bundle 106.The hood 112 includes an upper end 114 adjacent the upper portion 102 ofthe shell 100 above the tube bundle 106 and above the distributor 108.Extending from opposite ends of the upper end 114 toward the lowerportion 104 of the shell 100 are opposed substantially parallel walls116, in one embodiment the walls 116 extending substantially verticallyand terminating at an open end 118 that is substantially opposite theupper end 114. In one embodiment, the upper end 114 and parallel walls116 are closely disposed adjacent to the tubes of the tube bundle 106,with the parallel walls 116 extending sufficiently toward the lowerportion 104 of the shell 100 as to substantially laterally surround thetubes of the tube bundle 106. However, it is not required that theparallel walls 116 extend vertically past the lower tubes of the tubebundle 106, nor is it required that the parallel walls 116 are planar,although vapor refrigerant 122 that forms within the outline of the tubebundle 106 is channeled substantially vertically within the confines ofthe parallel walls 116 and through the open end 118 of the hood 112. Thehood 112 forces the vapor refrigerant 122 downward between the walls 116and through the open end 118, then upward in the space between the shell100 and the walls 116 from the lower portion 104 of the shell 100 to theupper portion 102 of the shell 100. The vapor refrigerant 122 then flowsover a pair of extensions 150 protruding adjacent to the upper end 114of the parallel walls 116 and into a suction channel 154. The vaporrefrigerant 122 enters into the suction channel 154 through slots 152which are spaces between the ends of the extensions 150 and the shell100 that define slots 152, before exiting the evaporator 80 at an outlet132 that is connected to the compressor 60.

Refrigerant 126 that is received from the condenser 70 and the lowerportion 104 of the shell 100 (liquid refrigerant 120) is directedthrough the distributor 108 and, as shown, deposited from a plurality ofpositions 110 onto the upper tubes of the tube bundle 106. Thesepositions 110 can include any combination of longitudinal or lateralpositions with respect to the tube bundle 106. In one embodiment,distributor 108 includes a plurality of nozzles supplied at least by aliquid ramp that is supplied by the condenser 70. The nozzles apply, inone embodiment, a predetermined jet pattern so that the upper row oftubes is covered. An amount of the refrigerant boils by virtue of theheat exchange that occurs along the tube surfaces of the tube bundle106. This expanding vapor refrigerant 122 is directed downwardly towardthe open end 118 since the upper end 114 of the hood 112 andsubstantially parallel walls 116 provide no alternate escape path.Since, as shown, the substantially parallel walls 116 are adjacent tothe outer column of tubes of the tube bundle 106, vapor refrigerant 122is forced substantially vertically downward, substantially preventingthe possibility of cross flow of the vapor refrigerant 122 inside thehood 112. The tubes of the tube bundle 106 are arranged to promote theflow of refrigerant in the form of a film around the tube surfaces, theliquid refrigerant coalescing to form droplets or, in some instances, acurtain or sheet of liquid refrigerant at the bottom of the tubesurfaces. The resulting sheeting promotes wetting of the tube surfaceswhich enhances the heat transfer efficiency between the fluid flowinginside the tubes of the tube bundle 106 and the refrigerant flowingaround the surfaces of the tubes of the tube bundle 106.

Unlike current systems, the upper end 114 of the hood 112 substantiallyprevents the flow of applied refrigerant 110, in the form of vapor andmist, at the top of the tube bundle 106 from flowing directly to theoutlet 132 which is fed to the compressor 60. Instead, by directing therefrigerant 122 to have a downwardly directed flow, the vaporrefrigerant 122 must travel downward through the length of thesubstantially parallel walls 116 before the refrigerant can pass throughthe open end 118. After the vapor refrigerant 122 passes the open end118 which contains an abrupt change in direction, the vapor refrigerant122 is forced to travel between the hood 112 and the inner surface ofthe shell 100. This abrupt directional change results in a greatproportion of any entrained droplets of refrigerant to collide witheither the liquid refrigerant 120 or the shell 100 or hood 112, removingthose droplets from the vapor refrigerant 122 flow. Also, refrigerantmist traveling the length of the substantially parallel walls 116 iscoalesced into larger drops that are more easily separated by gravity,or evaporated by heat transfer on the tube bundle 106.

Once the vapor refrigerant 122 passes through the parallel walls 116 ofthe hood 112, the vapor refrigerant 122 then flows from the lowerportion 104 to the upper portion 102 along the prescribed narrowpassageway, and, as shown, substantially symmetric passageways, formedbetween the surfaces of the hood 112 and the shell 100 prior to reachingthe outlet 132. As a result of the increased drop size, the efficiencyof liquid separation by gravity is improved, permitting an increasedupward velocity of vapor refrigerant 122 flow through the evaporator. Abaffle is provided adjacent the evaporator outlet to prevent a directpath of the vapor refrigerant 122 to the compressor inlet. The baffleincludes slots 152 defined by the spacing between the ends of extensions150 and the shell 100. The combination of the substantially parallelwalls 116, narrow passageways and slots 152 in the evaporator 80 removesvirtually all the remaining entrained droplets from the vaporizedrefrigerant 122.

By substantially eliminating cross flow of vapor refrigerant andcoalesced drops of liquid refrigerant along tube bundle 106, the amountof refrigerant 120 that must be recirculated can be reduced. It is thereduction of the amount of recirculated refrigerant flow that can enablethe use of ejector 128, versus a conventional pump. The ejector 128combines the functions of an expansion device and a refrigerant pump. Inaddition, it is possible to incorporate all expansion functionality intothe distributor 108 nozzles. In one embodiment, two expansion devicesare employed: a first expansion device being incorporated into sprayingnozzles of the distributor 108. A second expansion device can also be apartial expansion in the liquid line 130, such as a fixed orifice, oralternately, a valve controlled by the level of liquid refrigerant 120,to account for variations in operating conditions, such as evaporatingand condensing pressures, as well as partial cooling loads. Further, inone embodiment, most of the expansion occurs in the nozzles, providing agreater pressure difference, while simultaneously permitting the nozzlesto be of reduced size, thereby reducing the size and cost of thenozzles.

Referring to FIG. 6, an embodiment of a hybrid falling film evaporator280 is presented which includes an immersed or at least partiallyimmersed tube bundle 207 in addition to a tube bundle 106. Except asdiscussed, corresponding components in evaporator 280 are otherwisesimilar to evaporator 80. In one embodiment, evaporator 280 incorporatesa two pass system in which fluid that is to be cooled first flows insidethe tubes of lower tube bundle 207 and then is directed to flow insidethe tubes of the upper tube bundle 106. Since the second pass of the twopass system occurs on the top tube bundle 106, the temperature of thefluid flowing in the tube bundle 106 is reduced, requiring a lesseramount of refrigerant flow over the surfaces of the tube bundle 106.Thus, there is no need to re-circulate refrigerant 120 to thedistributor 108. Also, the bundle 207 evaporates the extra refrigerantdropping from tube bundle 106. If there is no recirculation device,e.g., pump or ejector, the falling film evaporator must be a hybrid.

It is to be understood that although a two pass system is described inwhich the first pass is associated with an at least partially immersed(flooded) lower tube bundle 207 and the second pass associated withupper tube bundle 106 (falling film), other arrangements arecontemplated. For example, the evaporator can incorporate a one passsystem with any percentage of flooding associated with lower tube bundle207, the remaining portion of the one pass associated with upper tubebundle 106. Alternately, the evaporator can incorporate a three passsystem in which two passes are associated with lower tube bundle 207 andthe remaining pass associated with upper tube bundle 106, or in whichone pass is associated with lower tube bundle 207 and its remaining twopasses are associated with upper tube bundle 106. Further, theevaporator can incorporate a two pass system in which one pass isassociated with upper tube portion 106 and the second pass is associatedwith both the upper tube portion 106 and the lower tube portion 207. Insummary, any number of passes in which each pass can be associated withone or both of the upper tube bundle and the lower tube bundle iscontemplated.

While embodiments have been directed to refrigeration systems, theevaporator of the present application can also be used with processsystems, such as a chemical process involving a blend of two components,one being volatile such as in the petrochemical industry. Alternately,the process system could relate to the food processing industry. Forexample, the evaporator of the present application could be used tocontrol a juice concentration. Referring to FIG. 3, a juice (e.g.,orange juice) fed through the fluid distributor 108 is heated, a portionbecoming vapor, while the liquid 120 accumulating at the lower portionof the evaporator contains a higher concentration of juice. One skilledin the art can appreciate that the evaporator can be used for otherprocess systems.

In one embodiment, the walls 116 are parallel and the walls 116 aresymmetric about a central vertical plane 134 bisecting the upper andlower portions 102, 104, since the tube bundle 106 arrangements aretypically similarly symmetric.

The arrangement of tubes in tube bundles 106 is not shown, although atypical arrangement is defined by a plurality of uniformly spaced tubesthat are aligned vertically and horizontally, forming an outline thatcan be substantially rectangular. However, a stacking arrangementwherein the tubes are neither vertically or horizontally aligned mayalso be used, as well as arrangements that are not uniformly spaced.

In addition or in combination with other features of the presentapplication, different tube bundle constructions are contemplated. Forexample, it is possible to reduce the volume of the shell 100 if therefrigerant is deposited by the distributor 108 at wide angles. However,such wide angles can create deposited refrigerant having horizontalvelocity components, possibly generating an uneven longitudinal liquiddistribution. To address this issue, finned tubes (not shown), as areknown in the art, can be used along the uppermost horizontal row oruppermost portion of the tube bundle 106. Besides possibly using finnedtubes on top, the straightforward approach is to use new generationenhanced tube developed for pool boiling in flooded evaporators.Additionally, or in combination with the finned tubes, porous coatings,as are known in the art, can also be applied to the outer surface of thetubes of the tube bundles 106.

Referring to FIG. 8, which is generic to both evaporator constructionsof the present application, a hood 112 has substantially vertical walls116 that substantially prevents cross flow caused by expandingvaporizing refrigerant fluid 122, facilitating increased heat transferwith a minimum re-circulation rate. In addition, as previouslydiscussed, the vapor refrigerant 122, passes through the parallel walls116 of the hood 112 and then flows from the lower portion 104 to theupper portion 102 along the prescribed narrow passageway formed betweenthe surfaces of the hood 112 and the shell 100 prior to reaching theoutlet 132. As a result of the increased drop size, the efficiency ofliquid separation by gravity is improved, permitting an increased upwardvelocity of vapor refrigerant 122 flow through the evaporator. A baffleis provided adjacent the evaporator outlet to prevent a direct path ofthe vapor refrigerant 122 to the compressor inlet. The baffle includesslots 152 defined by the spacing between the ends of extensions 150 andthe shell 100. The combination of the substantially parallel walls 116,narrow passageways and slots 152 in the evaporator 80 removes virtuallyall the remaining entrained droplets from the vaporized refrigerant 122.

To further improve the efficiency of liquid separation, as shown in FIG.8, a flow distributor 300 is disposed adjacent to the open end 118between hood 112 and shell 100. Flow distributor 300 modifies therefrigerant flow between hood 112 and the shell 100 to provide a moreuniform refrigerant flow distribution. Due to the more uniformrefrigerant flow distribution, the velocity of vapor refrigerant 122 isreduced, improving the efficiency of liquid separation by gravity.

Referring to FIGS. 9-12, several embodiments of flow distributors arediscussed. For example, as shown in FIG. 9, flow distributor 302 is inthe form of a guide vane that is angled with respect to wall 116. Asshown in FIG. 10, guide vane 302 has a curved profile. Although the flowdistributors 302 are shown disposed between wall 116 and lower portion104 of shell 100, it is to be understood that the flow distributors canextend from either wall 116 or the shell or from both. Further, throughapertures can be formed in flow distributors 302.

Referring to FIG. 11, flow distributor 304 is a plate extending towardwall 116 and disposed substantially perpendicular to wall 116, andcontaining a plurality of through apertures. In one embodiment, flowdistributor 302 includes apertures of different sizes, with smallerthrough apertures being disposed on portions of the flow distributorthat is adjacent to shell 100. In another embodiment, flow distributor302 is a wire mesh. Referring to FIG. 12, flow distributor 302 includesa combination of a guide vane and a plate 304.

It is to be understood that embodiments of flow distributors can includeany combination of elements disposed anywhere along the lower portion104 of shell, such as between wall 116 and shell 100 that act to improveliquid separation of the refrigerant flow 122 and provide more uniformflow velocities by redirecting the flow of refrigerant. In addition,flow distributors can exhibit porosity, for example, non-woven wire meshor an alternate structural arrangement, such as honeycomb.

It is also understood that the various embodiments of flow distributorcan also be used with applications outside of refrigeration systems, aspreviously discussed.

In another embodiment (FIG. 13) the hood is asymmetrically disposedwithin the evaporator, with more than one half of the flow ofrefrigerant flowing beneath the one side disposed further from theshell. As shown, substantially all of the refrigerant flowing is beneathone side of the hood.

Surface textures can be advantageous for the hood, i.e., smooth versuspitted or scuffed surfaces. The shape and structure of the roof top ofthe hood can be important for the following reasons: 1) it is desiredthat the distribution of liquid over the tubes be as uniform aspossible; 2) the spray nozzles and impact on the tubes generate somemist that will strike the roof. From there, the liquid may fall back ina totally uncontrolled way. For instance, as shown in FIG. 6, the liquidthat reaches the roof of the hood is likely due to capillary action,then reach the vertical walls of the hood and fall to the bottom part ofthe hood without contributing to wetting the walls of the bundle 106.FIG. 7 would produce liquid droplets to fall in an arrangement still farfrom uniform, but must be better than FIG. 6, because the liquid will atleast drip upon the outer columns of tubes, and will not be lost. Moresophisticated designs are possible, such as a substantially horizontalroof having multiple ripples (FIG. 14) dripping above each column oftubes to bundle 106, although other arrangements are possible. Forexample, in an alternate embodiment as shown in FIG. 15, taken alongline 17-17 of FIG. 14, ripples or surface discontinuities sufficient todistribute liquid refrigerant from the roof of the hood can extendsubstantially transverse to the direction of the tubes of tube bundle106. Alternatively, the ripples or surface discontinuities can extend atan angle to the direction of the tubes of tube bundle 106. However, itis appreciated that the ripples or discontinuities can be non-linear andnon-uniform in profile. In addition, the roof of the hood can havecoatings of material applied to the surface to achieve the desired flowof liquid refrigerant or in combination with shaped profiles of the roofof the hood. The vapor refrigerant 122 then flows over a pair ofextensions 150 protruding adjacent to the upper end 114 of the parallelwalls 116 and into a suction channel 154. The vapor refrigerant 122enters into the suction channel 154 through slots 152 which are spacesbetween the ends of the extensions 150 and the shell 100 that defineslots 152, before exiting the evaporator 80 at an outlet 132 that isconnected to the compressor 60.

Unlike current systems, the upper end 114 of the hood 112 substantiallyprevents the flow of applied refrigerant 110, in the form of vapor andmist, at the top of the tube bundle 106 from flowing directly to theoutlet 132, which is fed to the compressor 60. Instead, by directing therefrigerant 122 to have a downwardly directed flow, the vaporrefrigerant 122 must travel downward through the length of thesubstantially parallel walls 116 before the refrigerant can pass throughthe open end 118. After the vapor refrigerant 122 passes the open end118, which contains an abrupt change in direction, the vapor refrigerant122 is forced to travel between the hood 112 and the inner surface ofthe shell 100. This abrupt directional change results in a greatproportion of any entrained droplets of refrigerant to collide witheither the liquid refrigerant 120 or the shell 100 or hood 112, removingthose droplets from the vapor refrigerant 122 flow. Also, refrigerantmist traveling the length of the substantially parallel walls 116 iscoalesced into larger drops that are more easily separated by gravity,or evaporated by heat transfer on the tube bundle 106.

It is to be understood that although a two pass system is described inwhich the first pass is associated with an at least partially immersed(flooded) lower tube bundle 207 and the second pass associated withupper tube bundle 106 (falling film), other arrangements arecontemplated. For example, the evaporator can incorporate a one passsystem with any percentage of flooding associated with lower tube bundle207, the remaining portion of the one pass associated with upper tubebundle 106. Alternately, the evaporator can incorporate a three passsystem in which two passes are associated with lower tube bundle 207 andthe remaining pass associated with upper tube bundle 106, or in whichone pass is associated with lower tube bundle 207 and its remaining twopasses are associated with upper tube bundle 106. Further, theevaporator can incorporate a two pass system in which one pass isassociated with upper tube portion 106 and the second pass is associatedwith both the upper tube portion 106 and the lower tube portion 207. Insummary, any number of passes in which each pass can be associated withone or both of the upper tube bundle and the lower tube bundle iscontemplated.

It should be understood that the application is not limited to thedetails or methodology set forth in the following description orillustrated in the figures. It should also be understood that thephraseology and terminology employed herein is for the purpose ofdescription only and should not be regarded as limiting.

While the exemplary embodiments illustrated in the figures and describedherein are presently preferred, it should be understood that theseembodiments are offered by way of example only. Accordingly, the presentapplication is not limited to a particular embodiment, but extends tovarious modifications that nevertheless fall within the scope of theappended claims. The order or sequence of any processes or method stepsmay be varied or re-sequenced according to alternative embodiments.

It is important to note that the construction and arrangement of theevaporator as shown in the various exemplary embodiments is illustrativeonly. Although only a few embodiments have been described in detail inthis disclosure, those skilled in the art who review this disclosurewill readily appreciate that many modifications are possible (e.g.,variations in sizes, dimensions, structures, shapes and proportions ofthe various elements, values of parameters, mounting arrangements, useof materials, colors, orientations, etc.) without materially departingfrom the novel teachings and advantages of the subject matter recited inthe claims. For example, elements shown as integrally formed may beconstructed of multiple parts or elements, the position of elements maybe reversed or otherwise varied, and the nature or number of discreteelements or positions may be altered or varied. Accordingly, all suchmodifications are intended to be included within the scope of thepresent application. The order or sequence of any process or methodsteps may be varied or re-sequenced according to alternativeembodiments. In the claims, any means-plus-function clause is intendedto cover the structures described herein as performing the recitedfunction and not only structural equivalents but also equivalentstructures. Other substitutions, modifications, changes and omissionsmay be made in the design, operating conditions and arrangement of theexemplary embodiments without departing from the scope of the presentapplication.

1. A refrigeration system comprising: a compressor, a condenser, anexpansion device and an evaporator connected in a closed refrigerantloop; and the evaporator comprising: a shell having an upper portion anda lower portion; a tube bundle, the tube bundle having a plurality oftubes extending substantially horizontally in the shell; a hood disposedover the tube bundle, the hood having a closed end and an open endopposite the closed end, the closed end being disposed above the tubebundle adjacent the upper portion of the shell, the hood further havingopposed substantially parallel walls extending from the closed portiontoward the open portion of the shell; a refrigerant distributor disposedbelow the hood and above the tube bundle, the refrigerant distributorbeing configured to deposit liquid refrigerant or liquid and vaporrefrigerant onto the tube bundle, the substantially parallel walls ofthe hood substantially prevent cross flow of the refrigerant between theplurality of tubes of the tube bundle; a flow distributor disposedadjacent the open end between the hood and the shell; and wherein theflow distributor modifies the refrigerant flow between the hood and theshell to provide a more uniform refrigerant flow distribution.
 2. Therefrigerant system of claim 1 wherein the flow distributor is angledfrom a hood wall.
 3. The refrigerant system of claim 2 wherein the flowdistributor extends from the hood wall.
 4. The refrigerant system ofclaim 2 wherein the flow distributor extends from the shell.
 5. Therefrigerant system of claim 1 wherein the flow distributor is curved. 6.The refrigerant system of claim 1 wherein the flow distributor includesa plurality of through apertures.
 7. The refrigerant system of claim 6wherein the flow distributor extends between the hood wall and theshell.
 8. A falling film evaporator for use in a refrigeration systemcomprising: a shell having an upper portion and a lower portion; a tubebundle, the tube bundle having a plurality of tubes extendingsubstantially horizontally in the shell; a hood disposed over the tubebundle, the hood having a closed end and an open end opposite the closedend, the closed end being disposed above the tube bundle adjacent theupper portion of the shell, the hood further having opposedsubstantially parallel walls extending from the closed portion towardthe open portion of the shell; a refrigerant distributor disposed belowthe hood and above the tube bundle, the refrigerant distributor beingconfigured to deposit liquid refrigerant or liquid and vapor refrigerantonto the tube bundle, the substantially parallel walls of the hoodsubstantially prevent cross flow of the refrigerant between theplurality of tubes of the tube bundle; a flow distributor disposedadjacent the open end between the hood and the shell; and wherein theflow distributor modifies the refrigerant flow between the hood and theshell to provide a more uniform refrigerant flow distribution.
 9. Thefalling film evaporator of claim 8 wherein the flow distributor isangled from a hood wall.
 10. The falling film evaporator of claim 9wherein the flow distributor extends from the hood wall.
 11. The fallingfilm evaporator of claim 9 wherein the flow distributor extends from theshell.
 12. The falling film evaporator of claim 8 wherein the flowdistributor is curved.
 13. The falling film evaporator of claim 8wherein the flow distributor includes a plurality of through apertures.14. The falling film evaporator of claim 13 wherein the flow distributorextends between the hood wall and the shell.
 15. A hybrid falling filmevaporator for use in a refrigeration system comprising: a shell havingan upper portion and a lower portion; a lower tube bundle in fluidcommunication with an upper tube bundle, the lower and upper tubebundles each having a plurality of tubes extending substantiallyhorizontally in the shell, the lower tube bundle being at leastpartially submerged by refrigerant in the lower portion of the shell; ahood disposed over the upper tube bundle, the hood having a closed endand an open end opposite the closed end, the closed end being adjacentthe upper portion of the shell above the upper tube bundle, the hoodfurther having opposed substantially parallel walls extending from theclosed end toward the open end adjacent the lower portion of the shell;a refrigerant distributor, the refrigerant distributor being disposedabove the upper tube bundle, the refrigerant distributor depositingrefrigerant onto the upper tube bundle; the substantially parallel wallsof the hood substantially preventing cross flow of refrigerant betweenthe plurality of tubes of the upper tube bundle; a flow distributordisposed adjacent the open end between the hood and the shell; andwherein the flow distributor modifies the refrigerant flow between thehood and the shell to provide a more uniform refrigerant flowdistribution.
 16. The falling film evaporator of claim 15 wherein theflow distributor is a member angled from a hood wall.
 17. The fallingfilm evaporator of claim 16 wherein the flow distributor extends fromthe hood wall.
 18. The falling film evaporator of claim 16 wherein theflow distributor extends from the shell.
 19. The falling film evaporatorof claim 15 wherein the flow distributor is curved.
 20. The falling filmevaporator of claim 15 wherein the flow distributor includes a pluralityof through apertures.
 21. The falling film evaporator of claim 20wherein the flow distributor extends between the hood wall and theshell.
 22. A falling film evaporator for use in a control processcomprising: a shell having an upper portion and a lower portion; a tubebundle, the tube bundle having a plurality of tubes extendingsubstantially horizontally in the shell; a hood disposed over the tubebundle, the hood having a closed end and an open end opposite the closedend, the closed end being disposed above the tube bundle adjacent theupper portion of the shell, the hood further having opposedsubstantially parallel walls extending toward the lower portion of theshell; a fluid distributor disposed below the hood and above the tubebundle, the fluid distributor being configured to deposit liquid fluidor liquid and vapor fluid onto the tube bundle; the substantiallyparallel walls of the hood substantially preventing cross flow of thefluid between the plurality of tubes of the tube bundle; a flowdistributor disposed adjacent the open end between the hood and theshell; and wherein the flow distributor modifies the refrigerant flowbetween the hood and the shell to provide a more uniform refrigerantflow distribution.
 23. A falling film evaporator for use in arefrigeration system comprising: a shell having an upper portion and alower portion; a tube bundle, the tube bundle having a plurality oftubes extending substantially horizontally in the shell; a hood disposedover the tube bundle, the hood having a closed end and an open endopposite the closed end, the closed end being disposed above the tubebundle adjacent the upper portion of the shell, the hood further havingopposed substantially parallel walls extending from the closed portiontoward the open portion of the shell; and wherein the hood isasymmetrically disposed within the evaporator.
 24. A falling filmevaporator for use in a refrigeration system comprising: a shell havingan upper portion and a lower portion; a tube bundle, the tube bundlehaving a plurality of tubes extending substantially horizontally in theshell; a hood disposed over the tube bundle, the hood having a closedend and an open end opposite the closed end, the closed end beingdisposed above the tube bundle adjacent the upper portion of the shell,the hood further having opposed substantially parallel walls extendingfrom the closed portion toward the open portion of the shell; andwherein the hood includes surface textures.
 25. The falling filmevaporator of claim 24 wherein a roof of the hood includes surfacediscontinuities sufficient to distribute liquid refrigerant therefrom.